1. Field of the Invention
The present invention relates to memory devices and methods for manufacturing memory devices, and more particularly to high density three-dimensional (3D) memory devices having a plurality of programmable resistive memory elements based on metal-oxygen compounds.
2. Description of Related Art
Metal oxide based nonvolatile resistive random access memory RRAM has attracted much attention because of its simple structure and excellent properties such as low power, high speed, and a large memory window between resistive states.
Tungsten-oxygen WOx based RRAM can be caused to change resistance between two or more stable ranges by application of electrical pulses at levels suitable for implementation in integrated circuits, and the resistance can be read and written with random access to indicate stored data. See, U.S. patent application Ser. No. 11/955,137 entitled “Memory Devices Having an Embedded Resistance Memory with Tungsten Compound and Manufacturing Methods”, filed 12 Dec. 2007 and incorporated by reference herein.
Multi-level operation comprises changing the resistance of the metal-oxide material between more than two resistance states and is desirable since the data storage density can be increased.
Additionally, in order to achieve higher density it is desirable to reduce the cross-sectional area or footprint of individual memory cells in an array of memory cells. However, problems have arisen in manufacturing devices with very small dimensions, and with variations in manufacturing processes needed to meet the tight tolerance requirements necessary for large-scale high-density memory devices.
It is therefore desirable to provide a metal-oxide based memory cell structure for use in high-density memory devices having multi-level operation, as well as methods for manufacturing which address the tight process requirements needed for manufacturing large-scale high density devices.